[PATCH AUTOSEL 3.18 16/22] ext4: fix argument checking in EXT4_IOC_MOVE_EXT

[Sasha Levin]

From: Theodore Ts'o <tytso@xxxxxxx>

[ Upstream commit f18b2b83a727a3db208308057d2c7945f368e625 ]

If the starting block number of either the source or destination file
exceeds the EOF, EXT4_IOC_MOVE_EXT should return EINVAL.

Also fixed the helper function mext_check_coverage() so that if the
logical block is beyond EOF, make it return immediately, instead of
looping until the block number wraps all the away around.  This takes
long enough that if there are multiple threads trying to do pound on
an the same inode doing non-sensical things, it can end up triggering
the kernel's soft lockup detector.

Reported-by: syzbot+c61979f6f2cba5cb3c06@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Cc: stable@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/ext4/move_extent.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index 4d1049517e4a..ebe809bac808 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -533,9 +533,13 @@ mext_check_arguments(struct inode *orig_inode,
 			orig_inode->i_ino, donor_inode->i_ino);
 		return -EINVAL;
 	}
-	if (orig_eof < orig_start + *len - 1)
+	if (orig_eof <= orig_start)
+		*len = 0;
+	else if (orig_eof < orig_start + *len - 1)
 		*len = orig_eof - orig_start;
-	if (donor_eof < donor_start + *len - 1)
+	if (donor_eof <= donor_start)
+		*len = 0;
+	else if (donor_eof < donor_start + *len - 1)
 		*len = donor_eof - donor_start;
 	if (!*len) {
 		ext4_debug("ext4 move extent: len should not be 0 "
-- 
2.17.1